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		<h1 id="0075-nodes-n-noodles-ii--mouse-noodling">0075: Nodes-n-noodles II – Mouse Noodling</h1>

<p>We’re still working our way through <em>Phase One</em> of this nodes-n-noodles concept and this time around, we’ll leave static noodles behind and get some animation happening.</p>

<h2 id="controlling-the-noodle-with-the-mouse">Controlling the Noodle with the Mouse</h2>

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		The code file for this example is available <a href="https://github.com/rontarrant/gtkd_demos/blob/master/023_nodes/nodes_02_cubic_bezier_follow_mouse.d" target="_blank">here</a>.
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<p>The next step toward drawing a noodle connection between nodes entails two things:</p>

<ul>
  <li>using the mouse position as the curve’s end point, and</li>
  <li>taking control of window redraw (animation).</li>
</ul>

<p>To that end, we’re going to borrow from an earlier <em>Cairo</em> animation example <a href="./0064-cairo-vii-drawingarea-animation.html">Blog Post #0064</a> as well as the mouse tracker example <a href="./0015-enter-leave.html">Blog Post #0015</a> we looked at back in March.</p>

<p>From these earlier examples, we’re reminded that:</p>

<ul>
  <li>the mouse pointer’s position is supplied by the <code class="language-plaintext highlighter-rouge">onMotionNotify</code> signal, and</li>
  <li>gaining control over window redraw means working with a <code class="language-plaintext highlighter-rouge">Timeout</code> object.</li>
</ul>

<h2 id="draw-and-redraw">Draw and Redraw</h2>

<p>The <code class="language-plaintext highlighter-rouge">Timeout</code> object, <a href="https://github.com/rontarrant/gtkd_demos/blob/master/018_cairo/cairo_24_counter_animation.d">as we saw before</a>, decides when we’ll call a function similar to this example’s <code class="language-plaintext highlighter-rouge">onFrameElapsed()</code> function (which is taken, unchanged, from <a href="https://github.com/rontarrant/gtkd_demos/blob/master/005_mouse/mouse_04_tracker.d">the mouse tracker</a> example):</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">bool</span> <span class="n">onFrameElapsed</span><span class="p">()</span>
<span class="p">{</span>
	<span class="n">GtkAllocation</span> <span class="n">size</span><span class="p">;</span>
	<span class="n">getAllocation</span><span class="p">(</span><span class="n">size</span><span class="p">);</span>
		
	<span class="n">queueDrawArea</span><span class="p">(</span><span class="n">size</span><span class="p">.</span><span class="n">x</span><span class="p">,</span> <span class="n">size</span><span class="p">.</span><span class="n">y</span><span class="p">,</span> <span class="n">size</span><span class="p">.</span><span class="n">width</span><span class="p">,</span> <span class="n">size</span><span class="p">.</span><span class="n">height</span><span class="p">);</span>
		
	<span class="k">return</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// onFrameElapsed()</span>
</code></pre></div></div>

<p>What it does is:</p>

<ul>
  <li>instantiate a <code class="language-plaintext highlighter-rouge">GtkAllocation</code> object from which we…</li>
  <li>extract the size of the <code class="language-plaintext highlighter-rouge">DrawingArea</code>, and</li>
  <li>call for a redraw.</li>
</ul>

<h3 id="the-cubic-beziers-starting-point">The Cubic Bezier’s Starting Point</h3>

<p>For now, we’ll use a hard-coded starting point and turn our attention to another problem…</p>

<h3 id="grabbing-the-mouse-pointer-position">Grabbing the Mouse Pointer Position</h3>

<p>We can use the <code class="language-plaintext highlighter-rouge">onMotion()</code> function from <a href="https://github.com/rontarrant/gtkd_demos/blob/master/005_mouse/mouse_04_tracker.d">the mouse tracker example</a> to grab the mouse pointer position and use those x/y coordinates, along with the hard-coded starting point coordinates, to set our control points. From the previous post in this series, here’s a reminder of what those control point coordinates will be:</p>

<ul>
  <li>the coordinates of the first control point are:
    <ul>
      <li><code class="language-plaintext highlighter-rouge">x</code> is the same as the end point’s x,</li>
      <li><code class="language-plaintext highlighter-rouge">y</code> is the same as the start point’s y,</li>
    </ul>
  </li>
  <li>the second control point’s coordinates:
    <ul>
      <li><code class="language-plaintext highlighter-rouge">x</code> is the same as the start point’s x, and</li>
      <li><code class="language-plaintext highlighter-rouge">y</code> is the same as the end point’s y.</li>
    </ul>
  </li>
</ul>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">public</span> <span class="kt">bool</span> <span class="n">onMotion</span><span class="p">(</span><span class="n">Event</span> <span class="n">event</span><span class="p">,</span> <span class="n">Widget</span> <span class="n">widget</span><span class="p">)</span>
<span class="p">{</span>
	<span class="c1">// make sure we're not reacting to the wrong event</span>
	<span class="k">if</span><span class="p">(</span><span class="n">event</span><span class="p">.</span><span class="n">type</span> <span class="p">==</span> <span class="n">EventType</span><span class="p">.</span><span class="n">MOTION_NOTIFY</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="c1">// get the curve's end point</span>
		<span class="n">xEnd</span> <span class="p">=</span> <span class="n">event</span><span class="p">.</span><span class="n">motion</span><span class="p">.</span><span class="n">x</span><span class="p">;</span>
		<span class="n">yEnd</span> <span class="p">=</span> <span class="n">event</span><span class="p">.</span><span class="n">motion</span><span class="p">.</span><span class="n">y</span><span class="p">;</span>
			
		<span class="c1">// Recalculate the control points so we always have</span>
		<span class="c1">// a nice-looking double curve.</span>
		<span class="n">controlPointX1</span> <span class="p">=</span> <span class="n">xEnd</span><span class="p">;</span>
		<span class="n">controlPointY1</span> <span class="p">=</span> <span class="n">yStart</span><span class="p">;</span>
		<span class="n">controlPointX2</span> <span class="p">=</span> <span class="n">xStart</span><span class="p">;</span>
		<span class="n">controlPointY2</span> <span class="p">=</span> <span class="n">yEnd</span><span class="p">;</span>
	<span class="p">}</span>

	<span class="k">return</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// onMotion()</span>
</code></pre></div></div>

<p>And indeed, in the <code class="language-plaintext highlighter-rouge">onMotion()</code> function, we’re doing just that. After grabbing the mouse pointer position to use as the curve’s end point (<code class="language-plaintext highlighter-rouge">xEnd</code>/<code class="language-plaintext highlighter-rouge">yEnd</code>), we set the <code class="language-plaintext highlighter-rouge">controlPoints</code> and we’re ready to draw the curve. And the drawing itself is handled by the <code class="language-plaintext highlighter-rouge">onDraw()</code> function.</p>

<h3 id="how-the-ondraw-function-changes">How the onDraw() Function Changes</h3>

<p>Two things change in <code class="language-plaintext highlighter-rouge">onDraw()</code>:</p>

<ul>
  <li>a <code class="language-plaintext highlighter-rouge">Timeout</code> object is harnessed to set the redraw rate in frames per second, and</li>
  <li>instantiation of the control point coordinates has moved up to the preamble section of the <code class="language-plaintext highlighter-rouge">MyDrawingArea</code> class.</li>
</ul>

<p>And that leaves the <code class="language-plaintext highlighter-rouge">onDraw()</code> function looking like this:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">bool</span> <span class="n">onDraw</span><span class="p">(</span><span class="n">Scoped</span><span class="p">!</span><span class="n">Context</span> <span class="n">context</span><span class="p">,</span> <span class="n">Widget</span> <span class="n">w</span><span class="p">)</span>
<span class="p">{</span>
	<span class="k">if</span><span class="p">(</span><span class="n">_timeout</span> <span class="k">is</span> <span class="kc">null</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">_timeout</span> <span class="p">=</span> <span class="k">new</span> <span class="n">Timeout</span><span class="p">(</span><span class="n">fps</span><span class="p">,</span> <span class="p">&amp;</span><span class="n">onFrameElapsed</span><span class="p">,</span> <span class="kc">false</span><span class="p">);</span>
	<span class="p">}</span>

	<span class="c1">// set up and draw a cubic Bezier</span>
	<span class="n">context</span><span class="p">.</span><span class="n">setLineWidth</span><span class="p">(</span><span class="mi">3</span><span class="p">);</span>
	<span class="n">context</span><span class="p">.</span><span class="n">setSourceRgb</span><span class="p">(</span><span class="mf">0.3</span><span class="p">,</span> <span class="mf">0.2</span><span class="p">,</span> <span class="mf">0.1</span><span class="p">);</span>
	<span class="n">context</span><span class="p">.</span><span class="n">moveTo</span><span class="p">(</span><span class="n">xStart</span><span class="p">,</span> <span class="n">yStart</span><span class="p">);</span>
	<span class="n">context</span><span class="p">.</span><span class="n">curveTo</span><span class="p">(</span><span class="n">controlPointX1</span><span class="p">,</span> <span class="n">controlPointY1</span><span class="p">,</span> <span class="n">controlPointX2</span><span class="p">,</span> <span class="n">controlPointY2</span><span class="p">,</span> <span class="n">xEnd</span><span class="p">,</span> <span class="n">yEnd</span><span class="p">);</span>
	<span class="n">context</span><span class="p">.</span><span class="n">stroke</span><span class="p">();</span>

	<span class="k">return</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// onDraw()</span>
</code></pre></div></div>

<p>And the <code class="language-plaintext highlighter-rouge">MyDrawingArea</code> preamble now looks like:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">Timeout</span> <span class="n">_timeout</span><span class="p">;</span>
<span class="kt">int</span> <span class="n">fps</span> <span class="p">=</span> <span class="mi">1000</span> <span class="p">/</span> <span class="mi">24</span><span class="p">;</span> <span class="c1">// 24 frames per second</span>
<span class="kt">double</span> <span class="n">xStart</span> <span class="p">=</span> <span class="mi">25</span><span class="p">,</span> <span class="n">yStart</span> <span class="p">=</span> <span class="mi">128</span><span class="p">;</span>
<span class="kt">double</span> <span class="n">xEnd</span><span class="p">,</span> <span class="n">yEnd</span><span class="p">;</span>
<span class="kt">double</span> <span class="n">controlPointY1</span> <span class="p">=</span> <span class="mi">128</span><span class="p">,</span> <span class="n">controlPointX2</span> <span class="p">=</span> <span class="mi">25</span><span class="p">;</span>
<span class="kt">double</span> <span class="n">controlPointX1</span><span class="p">,</span> <span class="n">controlPointY2</span><span class="p">;</span>
</code></pre></div></div>

<h3 id="the-constructor">The Constructor</h3>

<p>As with the previous example, the constructor remains lean:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">this</span><span class="p">()</span>
<span class="p">{</span>
	<span class="n">addOnDraw</span><span class="p">(&amp;</span><span class="n">onDraw</span><span class="p">);</span>
	<span class="n">addOnMotionNotify</span><span class="p">(&amp;</span><span class="n">onMotion</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// this()</span>
</code></pre></div></div>

<p>Hook up the signals and we’re done.</p>

<h2 id="conclusion">Conclusion</h2>

<p>So there you have it, run the example and move the mouse around within the window. The curve redraws as the mouse moves and always describes a cubic <em>Bezier</em> curve.</p>

<p>Next time, we’ll take another step wherein a mouse button is clicked to start the drawing of the curve.</p>

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